This half-time, one-year research program comprises three biometric studies of human fertility, two of them being extensions of on-going projects supported by NICHD. First, in collaboration with the Cholera Research Laboratory, Dacca, Bangladesh, is a mathematical investigation of three contraceptive acceptance strategies. Second is an investigation of temporary separations as a determinant of marital fertility. A third study concerns sex preselection by selective abortion. In all three projects one or more probability models are developed and applied.